1. Field of the Invention
This invention relates to abrasive articles utilizing a binder which secures abrasive grains to a backing sheet, on fibers of a fibrous mat, or in a shaped mass, and to methods of making such articles utilizing a binder precursor that includes a reactive diluent.
2. Description of the Related Art
Coated abrasives generally comprise a flexible backing upon which a binder holds and supports a coating of abrasive grains. Coated abrasives typically employ a "make" coating comprising a resinous binder material. The make coating secures the abrasive grains to the backing. A "size" coating of resinous binder material applied over the make coating and abrasive grains firmly bonds the abrasive grains to the backing. Additionally, the abrasive grains are generally oriented with their longest dimension perpendicular to the backing to provide an optimum cut rate.
In a typical manufacturing process for making coated abrasives using thermally curable condensation binder precursors (for example resole phenolic resins), the make coating is formed from such a precursor composition, which is first applied to the backing. This is followed by electrostatic projection of abrasive grains into the make coating precursor. The make coating precursor is then partially thermally cured in order to set the abrasive grains. Next, a thermally curable condensation size coating precursor (which may be the same or different than the make coating precursor) is applied over the abrasive grains and make coating. Finally, the coating precursors are fully thermally cured.
U.S. Pat. No. 5,178,646 (Barber et al.) discloses thermally curable abrasive binder precursors containing reactive diluents. The thermally curable abrasive binder precursor containing reactive diluents may be blended with up to 50% by weight of an ethylenically unsaturated-monomer.
Non-woven abrasive articles typically comprise a fibrous web of synthetic and/or natural fibers which have on at least a portion of their surface an abrasive coating comprising abrasive grains and a binder which binds the fibers together. Binders and reactive diluents mentioned in the Barber et al. patent may be employed in the production of nonwoven abrasives.
In recent years radiation energy curable resins have been proposed as binders for coated abrasives as a substitute for conventional thermally curable condensation resins. Radiation energy curable resins can be cured much more rapidly than can thermally curable condensation resins. If additional heat is provided in an attempt to more rapidly cure phenolic resins, the viscosity of the phenolic resin will decrease, thereby resulting in loss of mineral orientation when used in make coatings.
The resinous adhesives used for abrasives production are preferably tailored such that they have cured properties desired for use as an abrasive article binder for each application. For example, in the coarse grade applications (larger particle sizes), the cured resinous adhesive(s) are most preferably hard, heat resistant and tough. Alternatively, in the fine grade applications (smaller particle sizes), the cured resinous adhesive(s) should be flexible and less hard.
One example of a typical resinous adhesive is a radiation curable aminoplast resin. The aminoplast resins have at least one pendant unsaturated group per molecule or oligomer. These unsaturated groups are preferably positioned .alpha.,.beta. with respect to the carbonyl moiety, and can be acrylate, methacrylate or acrylamide type groups. Examples of such materials include N-(hydroxymethyl)acrylamide, N,N'-oxydimethylenebisacrylamide, ortho and para acrylamidomethylated phenol, acrylamidomethylated phenolic novolak and combinations thereof. These materials are further described in U.S. Pat. Nos. 4,903,440, 5,055,113 and 5,236,472.
U.S. Pat. No. 4,588,419 (Caul et al.) describes radiation-curable coated abrasive material constructions in which acrylated epoxy and acrylated urethane resins are diluted with a number of monofunctional and polyfunctional acrylates as reactive diluents, including hexanediol diacrylate and trimethylolpropane triacrylate, as well as N-vinyl-2-pyrrolidone. The disclosed diluents, however, are not aromatic or polycyclic, and the acrylates are not effective solvents for aminoplast resins, and may not produce hard resins as preferred in the present application.
U.S. Pat. No. 4,927,431 (Buchanan, et al.) describes a resin binder for abrasive articles comprised of a blend of resole phenolic resin with a radiation-curable component containing pendant acrylate groups. The primary attribute of these cured blends is a hardness closer to that of phenolic resins and substantially higher than acrylate binders.
Thus, there is a need for reactive diluents which exhibit excellent solubility for acrylamide resins, which are highly reactive to both photochemical and thermal free-radical polymerization (defined as "addition polymerizable" herein), which exhibit low vapor pressures, which exhibit low viscosity at temperatures about 20.degree. C. and which enhance or, at the least, do not diminish the hardness of resins in which they are used. Copending U.S. application Ser. No 08/334,817 filed Nov. 4, 1994, now U.S. Pat. No. 5,523,152 which is a continuation-in-part application of U.S. application Ser. No. 08/143,824 filed Oct. 27, 1993, now abandoned, discloses such reactive diluents.